LetterEfficiency enhancement of the poly-silicon solar cell using self-assembled dielectric nanoparticles
Graphical abstract
Highlights
► This work provides a simple and truly economic way to boost the conversion efficiency of commercially available poly-silicon solar cells. ► Surface reflectance in UV and NIR is reduced with a layer of close-packed silica nanoparticles using a spin-coating technique. ► Optical properties of the self-assembled nanoparticle layers are simulated based on the rigorous coupled-wave analysis (RCWA) method.
Introduction
Silicon (Si) is the leading material used in the commercial production of low-cost solar cells. The development cost of solar cells can be further reduced by either reducing the manufacturing costs or by increasing the solar cell efficiency. Various cost-competitive, relatively cheaper processing steps have been developed to make these solar cells more energy efficient. Due to the fact that nanoparticles have the characteristics of light harvesting [1], [2], [3], [4], plasmon resonances and enhanced scattering [5], an appropriate and well-operated application of nanoparticles on the solar cells can therefore lead to high cell utility efficiency and provide low-cost production. Various solar cell substrates with nanoparticle deposits have been confirmed to enhance photocurrent [6] and acceptance angles [7] and improve the reflection of a specific wavelength (700–1100 nm) [8].
Recently, the scattering of incident light by nanoparticles has enabled the improved transmission of photons into the semiconductor active layers and the coupling of normally incident photons into the lateral, optically confined paths within the multiple-quantum-well waveguide layer, resulting in increased photon absorption, photocurrent generation, and power conversion efficiency of the solar cells [6]. Improvements in short-circuit current density (Jsc) have also been observed in quantum dot solar cells using silica and Au nanoparticles [8]. The scattering provided by the nanoparticles is believed to be essential for coupling and partially trapping light in substrate radiation modes. Although metallic nanoparticles provide efficient light scattering through coupling with surface plasmons, they exhibit extraordinary absorption at the surface plasmon resonances [9], significantly decreasing the overall effect of the metallic nanoparticles [10], [11]. Other than the metallic nanoparticles, dielectric nanoparticles with high dielectric permittivity can also be an alternative for sufficient light scattering. More importantly, some of the dielectric materials possess a relatively low dissipation level at visible wavelengths. Recently, the use of dielectric nanoparticles has been demonstrated theoretically to lead to similar and even higher enhancements compared to that of metallic nanoparticles [12].
Most of the previous research presented good nanoparticle performance with regard to flat-surface of devices. However, there is no report on the fabrication or tests on the properties of the textured surface of Si-based solar cell devices incorporated with self-assembled dielectric nanoparticles. In this paper, we report a comprehensive study of the nanoparticle-enhanced performance of poly-silicon solar cells using dielectric nanomaterial (silica nanospheres) with particle sizes ranging from 100 to 500 nm. Nanoparticle colloidal crystals were fabricated on the solar cell surface to achieve the optimum anti-reflection property by controlling the spin rate, spin duration, and particle concentration on a custom-built spin coater. Optical properties of the self-assembled nanoparticle layers were also simulated based on the rigorous coupled-wave analysis (RCWA) method. The simulation results were compared with the experimental results.
Section snippets
Experimental section
In this study, the poly-Si solar cell was prepared by following commercial fabrication processes. The p-type Si wafers were roughened using HF and HNO3 and showed damaged etch with no additional texturization. A 200 nm n-type layer was created on the texture by POCl3 diffusion using a centrotherm tube furnace to form the p–n junction, followed by the deposition of a thin anti-reflection layer of 80 nm SiNx using a centrotherm direct plasma PECVD furnace. The front and rear side finger and bus bar
Results and discussion
The enhanced light absorption, and hence the efficiency of light scattering into the silicon active layer, depends on the nanoparticle diameter, percentage surface coverage, and material permittivity. Based on earlier reports [11], [12] on maximizing the photocurrent response of solar cells, to achieve the best anti-reflection property from the self-assembled SNPs, there should be certain combinations of the diameter and areal density of the SNPs. To determine the best combination, we
Conclusions
In conclusion, we investigated the effects of dielectric scattering on absorption and photocurrent collection in the poly-Si solar cells decorated with self-assembled SNPs. With optimized nanoparticle parameters, such as size and surface coverage, enhanced light absorption in the UV and the NIR regions were observed. The power conversion efficiency of the poly-Si solar cell increased by 11.8% when 100 nm SNPs with a monolayer distribution were deposited on the textured surface of the cell. Our
Acknowledgment
This work was partially supported by the Bureau of Energy in Taiwan and National Science Council of Republic of China under Contract no. NSC 99-2119-M-009-004-MY3.
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